SDL2：快速像素操作

Question

我想在显示器上绘制像素，这些像素在某些参数后经常变化。例如。如果红色和绿色像素碰撞，它们都会消失，等等。

我必须在每一帧中处理大约 100 - 1000 个像素。我这里有一个多线程方法，它不会给我 30FPS（我想要的）。目前，我在 RAM 中存储了一个像素数组，其中包含所有像素并具有 SDL_Surface。当数组中的像素发生变化时，它也会在 Surface 中发生变化，然后在完成所有操作后被 blits 显示到屏幕上。我目前的方法太慢了，我想了想如何提高速度。

我目前的想法是：

使用 OpenGL 直接在 GPU 上进行像素操作，一些论坛告诉我这比我目前的方法慢得多 "this is not how a GPU works"
不存储像素数组，直接将 BMP 存储在 RAM 中，对其进行操作，然后将其移动到 SDL_Surface 或 SDL_Texture

有没有其他方法可以快速操作像素？

Answer 1

SDL_CreateTexture() w/SDL_TEXTUREACCESS_STREAMING + SDL_UpdateTexture() 似乎在正确的像素格式下工作得很好。

在我的系统上使用默认渲染器：

Renderer name: direct3d
Texture formats:
SDL_PIXELFORMAT_ARGB8888
SDL_PIXELFORMAT_YV12
SDL_PIXELFORMAT_IYUV

（尽管 opengl 信息相同:)

Renderer name: opengl
Texture formats:
SDL_PIXELFORMAT_ARGB8888
SDL_PIXELFORMAT_YV12
SDL_PIXELFORMAT_IYUV

SDL_PIXELFORMAT_ARGB8888 给我 ~1ms/frame:

// g++ main.cpp `pkg-config --cflags --libs sdl2`
#include <SDL.h>
#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <chrono>

void PrintFrameTiming(std::ostream& os = std::cout, float period = 2.0f)
{
    static unsigned int frames = 0;
    frames++;
    static auto start = std::chrono::steady_clock::now();
    auto end = std::chrono::steady_clock::now();

    float seconds = std::chrono::duration_cast< std::chrono::duration<float> >(end - start).count();
    if( seconds > period )
    {
        float spf = seconds / frames;
        os
            << frames << " frames in "
            << std::setprecision(1) << std::fixed << seconds << " seconds = "
            << std::setprecision(1) << std::fixed << 1.0f / spf << " FPS ("
            << std::setprecision(3) << std::fixed << spf * 1000.0f << " ms/frame)\n";
        frames = 0;
        start = end;
    }
}

int main( int, char** )
{
    SDL_Init( SDL_INIT_EVERYTHING );
    SDL_Window* window = SDL_CreateWindow( "SDL", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 600, 600, SDL_WINDOW_SHOWN );
    SDL_Renderer* renderer = SDL_CreateRenderer( window, -1, SDL_RENDERER_ACCELERATED );
    SDL_SetHint( SDL_HINT_RENDER_SCALE_QUALITY, "1" );
    
    // dump renderer info
    SDL_RendererInfo info;
    SDL_GetRendererInfo( renderer, &info );
    std::cout << "Renderer name: " << info.name << '\n';
    std::cout << "Texture formats: " << '\n';
    for( Uint32 i = 0; i < info.num_texture_formats; i++ )
    {
        std::cout << SDL_GetPixelFormatName( info.texture_formats[i] ) << '\n';
    }

    // create texture
    const unsigned int texWidth = 1024;
    const unsigned int texHeight = 1024;
    SDL_Texture* texture = SDL_CreateTexture( renderer, SDL_PIXELFORMAT_ARGB8888, SDL_TEXTUREACCESS_STREAMING, texWidth, texHeight );
    std::vector< unsigned char > pixels( texWidth * texHeight * 4, 0 );

    bool useLocktexture = false;

    // main loop
    bool running = true;
    while( running )
    {
        SDL_SetRenderDrawColor( renderer, 0, 0, 0, SDL_ALPHA_OPAQUE );
        SDL_RenderClear( renderer );

        // handle events
        SDL_Event ev;
        while( SDL_PollEvent( &ev ) )
        {
            if( ( SDL_QUIT == ev.type ) ||
                ( SDL_KEYDOWN == ev.type && SDL_SCANCODE_ESCAPE == ev.key.keysym.scancode ) )
            {
                running = false;
                break;
            }

            if( SDL_KEYDOWN == ev.type && SDL_SCANCODE_L == ev.key.keysym.scancode )
            {
                useLocktexture = !useLocktexture;
                std::cout << "Using " << ( useLocktexture ? "SDL_LockTexture() + std::copy_n()" : "SDL_UpdateTexture()" ) << '\n';
            }
        }
        
        // splat down some random pixels
        for( unsigned int i = 0; i < 1000; i++ )
        {
            const unsigned int x = rand() % texWidth;
            const unsigned int y = rand() % texHeight;

            const unsigned int offset = ( texWidth * y * 4 ) + x * 4;
            pixels[ offset + 0 ] = rand() % 256;        // b
            pixels[ offset + 1 ] = rand() % 256;        // g
            pixels[ offset + 2 ] = rand() % 256;        // r
            pixels[ offset + 3 ] = SDL_ALPHA_OPAQUE;    // a
        }

        // update texture
        if( useLocktexture )
        {
            unsigned char* lockedPixels = nullptr;
            int pitch = 0;
            SDL_LockTexture( texture, nullptr, reinterpret_cast< void** >( &lockedPixels ), &pitch );
            std::copy_n( pixels.data(), pixels.size(), lockedPixels );
            SDL_UnlockTexture( texture );
        }
        else
        {
            SDL_UpdateTexture( texture, nullptr, pixels.data(), texWidth * 4 );
        }

        SDL_RenderCopy( renderer, texture, nullptr, nullptr );
        SDL_RenderPresent( renderer );
        
        PrintFrameTiming();
    }

    SDL_DestroyRenderer( renderer );
    SDL_DestroyWindow( window );
    SDL_Quit();

    return 0;
}

确保你没有启用 vsync（在驱动程序中强制启用，运行合成器等）否则 all 你的帧时间将是~16ms（或任何你的显示刷新设置）。

SDL2：快速像素操作

SDL2: Fast Pixel Manipulation

c++

opengl

sdl

image-processing

sdl-2